Electronic cigarettes are typically battery-powered vaporizers that simulate the feeling of smoking, but without tobacco. Instead of cigarette smoke, the user inhales an aerosol, commonly called vapor, typically released by a heating element that atomizes a liquid solution (vaporizable material or solution). Typically, the user activates the e-cigarette by taking a puff or pressing a button. Some vaporizers look like traditional cigarettes, but they come in many variations.
Many electronic cigarettes use a pressure sensor to determine when the device should be heating or not. This may allow for an intuitive user interface where the user simply draws from (sucks on) the device to power it. It is advantageous over powering the device with a button in that the device's heating element is only powered when there is airflow over it assuming the device's pressure sensor and microcontroller can accurately detect the start and end of a draw.
Unfortunately, the vast majority of electronic cigarettes described and currently in use have an unexpected failure mode which may reduce the life of the battery and the overall device. Specifically, such devices may inadvertently (and transiently) detect a draw or inhalation following blowing or exhalation through the device. A recent test of numerous pressure sensor-based electronic cigarettes currently on the market found that these devices can easily be turned on and apply power to the heating element by blowing rather than inhaling into the mouthpiece of the device as if the user had drawn from the device. Specifically, such devices falsely indicate a draw (inhalation) and activate the heater at the end of a blow into the device because they detect a pressure drop at the end of the blow, and falsely interpret this is the start of a draw. Depending on the controller for the vaporizer, this pressure drop at the end of a blow may power the heater for some amount of time, and potentially until a timeout for max draw time. This failure mode may result in the device heating without the user drawing on it, which pay provide a non-ideal user experience, may waste of battery life and vaporizable material, and in devices without temp control may overheat the vaporizable material, which can produce e-juice degradants that taste bad and are potentially more harmful when vaporized that the original contents of the e-juice formulation.
Many commercially available electronic cigarettes use pressure sensors that are mechanically similar to electret microphones, but packaged with an ASIC (application specific integrated circuit) instead of a standard electret microphone circuit. An electret microphone is an electrostatic capacitor-based microphone that does not require a polarizing power supply. Pressure sensors of this type typically accept two power signals and have one output signal to indicate whether or not a pressure drop was recently detected. For the pressure sensor's ASIC to accommodate changes in environment conditions (humidity and temperature), slight differences in mechanical assembly from sensor to sensor, and potential shifting of parts in the mechanical assembly from vibration or drop, the ASIC's output usually depends on changes in capacitance between the sensor's conductive diaphragm (which deflects with a pressure differential across it) and a conductive static plate in the sensor instead of depending on absolute measured capacitance crossing some threshold. Given that not all measured pressure drops indicate that the user is drawing from the device, this approach is not ideal.
In all electronic cigarettes tested (some of which may not use the standard modified electret microphone with ASIC), the device can be made to start heating at the end of a blow into the device's air/vapor outlet. In devices in which direct capacitance measurements may be made by the microcontroller, the same behavior can be produced, meaning there is no software actively handling blows into the device correctly.
This failure mode may be largely unnoticed, but it is relevant based on many user practices. For example, some electronic cigarette users hold devices in their mouths, resulting in blowing into the device. Devices that don't adequately distinguish between drawing and the end of a blowing into the mouthpiece may start heating after a user has exhaled onto the device.
Described herein are apparatuses (systems and devices) and methods that may address the problem identified above.